1. Field of the Invention
The present invention relates to a charging device for charging a rechargeable battery. In particular, it relates to a charging device wherein a switching element is pulse-width modulated, thereby increasing or decreasing charging power.
2. Description of the Related Art
In a charging device, it is desirable for the charging power to be as large as the charging device can handle. The rechargeable battery is thus charged rapidly.
In charging devices, rated power is usually fixed, and adjustments of the charging power take place within the range of that rated power. Japanese Patent No. 3384079 sets forth a technique for distinguishing the number of battery cells contained in a battery pack to be charged, and determining a charging current based on the number of battery cells. When a battery pack with a large number of cells is to be charged, charging voltage is high, and consequently the charging current is reduced. When a battery pack with a small number of cells is to be charged, charging voltage is low, and consequently a large charging current is caused to flow. In this manner, the charging power is adjusted within the range of rated power of the charging device, and the charging current that is as large as possible within the range of rated power flows for charging the battery pack.